Carbon slurry regeneration method

ABSTRACT

A method for regenerating a carbon slurry used to produce a black matrix-type phosphor screen of a cathode ray tube is disclosed, in which excess carbon slurry is collected after the completion of a carbon-coating process onto a cathode ray tube panel. This collected carbon slurry is regenerated by means of an ion-exchange resin.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for regenerating a carbonslurry used to produce a black matrix-type phosphor screen of a colorcathode ray tube and to an apparatus for producing a black matrix-typephosphor screen of a cathode ray tube.

BACKGROUND OF THE INVENTION

A color cathode ray tube generally employs a black matrix-type phosphorscreen in which a light-absorption layer (so-called black matrix) isformed among red, green and blue phosphor stripes (or dots) in order toimprove the contrast thereof.

The black matrix-type phosphor screen is generally formed as follows.

As shown in FIG. 1A, the inner surface of a cathode ray tube panel 1 isfirst rinsed by an aqueous hydrofluoric acid solution. Then, a polyvinylalcohol type photosensitive film 2, made by adding ammonium dichromateto polyvinyl alcohol, is coated on the inner surface of the cathode raytube panel 1 and then dried.

As shown in FIG. 1B, a color selecting mechanism, for example, anaperture grill 3 is then used as an optical mask to expose thephotosensitive film 2 to ultraviolet rays. In this exposing process, thephotosensitive film 2 is exposed three times in the sequential order of,for example, green, blue and red colors. In FIG. 1B, reference numerals4R, 4G and 4B designate exposing light sources corresponding to the red,green and blue colors, respectively.

Thereafter, the photosensitive film 2 is developed by some suitableprocess such as rinsing with water or the like to obtain a resist layer,in this example, a resist layer 5 (5R, 5G, 5B) of stripe-configurationson the inner surface of the cathode ray tube panel 1 at positionscorresponding to the respective red, green and blue colors as shown inFIG. 1C.

After developing the film 2 with water, boric acid is dispensed onto thepanel including the resist layer 5, producing very straight edges on thePVA and thus eventually to the carbon stripes (see FIG. 1D). Then, theyare dried. This process will be hereinafter simply referred to as ahardening-process. In the hardening-process, a hardening agent usedthereon may be generally a boric acid aqueous solution, or other aqueoussolutions such as an aqueous tannic acid solution.

Then, as shown in FIG. 1E, a carbon slurry 6 is coated on the whole faceof the inner surface including the resist layers 5R, 5G and 5B, and thendried. At the next step, water 7 is sprayed to uniformly wet thecarbon-coated surface as shown in FIG. 1F. This wetting-process iscarried out in order to provide a buffer against the extremely strongoxidant which, upon application, soaks through the carbon layer anddissolves the underlying PVA by breaking up the polymerized chains, thusalso removing any carbon overlying it.

Then, the resist layer 5 is swollen and the developing-treatment isperformed by means of, for example, water-spray, to remove the resistlayer 5 and the carbon-coated layer formed on the resist layer 5, thuscarbon-stripes or black matrixes 8 of predetermined pattern are formedon the inner surface of the cathode ray tube panel 1 as shown in FIG.1G.

Thereafter, a phosphor slurry of, for example, green color is coatedthereon and dried. Then, the coated green phosphor slurry is exposed bymeans of the aperture grill 3 (see FIG. 1B) and developed so as to forma green phosphor stripe 9G on the inner surface of the cathode ray tubepanel 1 at its predetermined portion where the black matrix 8 is notformed. In a like manner, a blue phosphor stripe 9B and a red phosphorstripe 9R are formed on the inner surface of the cathode ray tube panel1 at its predetermined portions, thus a color phosphor screen 10 ofblack matrix-type is formed as shown in FIG. 1H.

In the above-mentioned carbon coating process, though not shown in thefigures, a carbon slurry from a carbon slurry tank is supplied through asupplying-system pipe to carbon-coating means, i.e., a nozzle. Thecarbon slurry is then ejected from the nozzle onto the inner surface ofthe cathode ray tube panel. After the carbon-coating film is uniformlycoated on the inner surface of the cathode ray tube panel, the excesscarbon slurry is collected back into the carbon slurry tank through acollection-system pipe.

Generally, when the carbon slurry used in this coating process iscollected and continuously recycled, the viscosity of the carbon slurryincreases. At a certain point in time, the carbon slurry becomesunsuitable for use in the coating process because the carbon-coated filmdoes not dry well after application to the Panel 1 because of theincrease in the viscosity of the carbon slurry. For example, if theviscosity of the carbon slurry is increased as high as four times itsoriginal viscosity, the thickness of the carbon-coated film is increasedthree times, making the carbon-coated film increasingly difficult to drybecause it does not dry evenly and sufficiently. When the carbon-coatedfilm that should be left in the afore-mentioned developing-process istoo viscous, there is undesirable peeling. This phenomenon occursespecially on the peripheral portions of the panel.

In the existing process, in order to control the viscosity of the carbonslurry so that it always falls in a constant range, each time the carbonslurry is coated on a predetermined number of panels, the carbon slurryexhaust port of the carbon slurry tank is opened to dump some of theslurry to allow a predetermined liquid level to remain in the tank.Thereafter, fresh carbon slurry is added to the carbon slurry tank up toits predetermined liquid level. This purging technique increases theamount of carbon slurry consumed. The manufacturing cost of the blackmatrix of the color cathode ray tube is inevitably increased.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amethod for regenerating a carbon slurry used to produce a blackmatrix-type phosphor screen of a cathode ray tube. Excess carbon slurry,left after the completion of a carbon-coating process onto a cathode raytube panel, is collected and then regenerated by contacting thecollected carbon slurry with ion-exchange resin.

According to another aspect of the present invention, there is providedan apparatus for producing a black matrix-type phosphor screen of acathode ray tube comprising: carbon coating means for coating a carbonslurry on a cathode ray tube panel; a tank for containing said carbonslurry; a supplying system for supplying said carbon slurry from saidcarbon slurry tank into said carbon coating means; a collecting systemfor collecting an extra carbon slurry produced from said carbon coatingmeans into said carbon slurry tank; and carbon slurry regenerating meansusing an ion-exchange resin, wherein said regenerating means is providedin at least one of said supplying system, said collecting system andsaid carbon slurry tank.

It is therefore an object of the present invention to provide animproved method for regenerating carbon slurry used to produce a blackmatrix-type phosphor screen of a cathode ray tube.

It is another object of the present invention to provide a method forregenerating a carbon slurry used to produce a black matrix-typephosphor screen of a cathode ray tube which can suppress an increase inthe viscosity of a carbon slurry.

It is still another object of the present invention to provide a methodfor regenerating a carbon slurry used to produce a black matrix-typephosphor screen of a cathode ray tube by which a collected carbon slurrycan be used repeatedly and cyclically.

It is a further object of the present invention to provide an improvedapparatus for producing a black matrix-type phosphor screen of a cathoderay tube.

It is a still further object of the present invention to provide anapparatus for producing a black matrix-type phosphor screen of a cathoderay tube which can suppress an increase in viscosity of a carbon slurry.

It is a still further object of the present invention to provide anapparatus for producing a black matrix-type phosphor screen of a cathoderay tube by which collected excess carbon slurry can be used repeatedlyand cyclically.

It is a yet further object of the present invention to provide anapparatus for producing a black matrix-type phosphor screen of a cathoderay tube which can decrease the manufacturing cost of a blackmatrix-type phosphor screen.

These, and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof the preferred embodiment, to be taken in conjunction with theaccompanying drawings, in which like reference numerals identify likeelements and parts.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A to 1H are schematic diagrams of prior art processes forproducing a black matrix-type phosphor screen and being useful forexplaining the present invention, respectively; and

FIG. 2 is a schematic diagram showing an embodiment of an apparatus forproducing a black matrix-type phosphor screen according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Prior to a description of a preferred embodiment of the invention, theprinciple of the present invention will be described briefly.

Although our invention is not to be limited by this explanation, it isour present understanding that the reason for an increased viscosity ofa carbon slurry collected after its application in a process forproducing a black matrix-type phosphor screen can be considered asfollows. Material coated on the inner surface of the panel before thecarbon slurry is coated on the inner surface becomes dissolved in thecollected carbon slurry. The carbon slurry is thereby aggregated so thatthe viscosity of the carbon slurry is increased. The materials whichbecome dissolved in the carbon slurry, are polyvinyl alcohols (PVA), anammonium dichromate (ADC), a boric acid and a tannic acid that act ashardening agents.

In accordance with the present invention, the carbon slurry which iscollected after the carbon slurry has been coated onto the cathode raytube panel having a hardening-processed resist layer formed on its innersurface is passed through an ion-exchange resin so that the dissolvedmaterial contained in the carbon slurry which contributes to itsincreased viscosity can be removed chemically. Thus, the viscosity ofthe collected carbon slurry can be decreased by chemical removal ofaggregation agents and thereby regenerated to have substantially thesame qualities as fresh carbon slurry.

With reference to the schematic diagram of FIG. 2, an example of anapparatus for producing a black matrix-type phosphor screen of a cathoderay tube that employs a method of regenerating a carbon slurry accordingto the present invention is described.

There is a cathode ray tube panel 11 on which is coated carbon slurry(and other components) that are used to produce a black matrix-typephosphor screen. This cathode ray tube panel 11 is rotatably supportedby a rotary arm 12. On the inner surface of the panel 11, there isformed a resist layer 5 of a predetermined pattern that has undergonethe hardening-treatment by means of, for example, the aqueous boric acidsolution as shown in, and described with reference to FIG. 1D.

Carbon slurry tank 13 accommodates a carbon slurry 14. The carbon slurrytank 13 incorporates therein stirring means 15 for stirring the carbonslurry 14. The carbon slurry 14 from the tank 13 is introduced through asupplying-system pipe 16 to a nozzle section 17 that serves as carboncoating means positioned in an opposing relation to the inner surface ofthe cathode ray tube panel 11. A pump 18 and a filter 19 are interposedon the supplying-system pipe 16 at its midway. On the side of thecathode ray tube panel 11, there is located a cover member 20 thatsurrounds the panel 11. Thus, of the carbon slurries ejected from thenozzle section 17 towards the inner surface of the cathode ray tubepanel 11, the excess carbon slurry 14 is stored in the lower portion ofthe cover member 20. The excess carbon slurry 14 is collected into thecarbon slurry tank 13 via a collecting-system pipe 21.

A pump 22 and a filter 23 are interposed on the collecting-system pipe21 at its midway. The filters 19 and 23 are adapted to remove materialsthat are aggregated in the carbon slurry by dusts and so on. In FIG. 2,reference numeral 24 designates a pipe for supplying new slurry into thecarbon slurry tank 13 and reference numeral 26 designates a pipe throughwhich the waste carbon slurry 14 within the carbon slurry tank 13 isabandoned to the outside of the tank 13. Reference numerals 25 and 27designate open and/or closed valves, respectively.

Accordingly, in this particularly preferred embodiment, a column 29filled with a negative ion-exchange resin is located in the midst of thecollecting-system pipe 21, particularly, at the position behind thefilter 23. This column 29 serves as carbon slurry regenerating meansbecause it chemically removes materials which lead to carbon aggregationand resulting viscosity increase.

The carbon slurry 14 used in this embodiment is a carbon slurry made bythe use of AQUADAG CARBON (tradename of carbon manufactured by AchesonJapan Limited.). The compositions of carbon solution and ready-mixedcarbon slurry solution are indicated in Table 1.

                  TABLE 1                                                         ______________________________________                                        Composition of Carbon Solution                                                Carbon solution    Ready-mixed carbon slurry                                  ______________________________________                                        Amount of solid carbon: 22%                                                                      Amount of solid carbon:                                                       5.5% to 7.5%                                               Organic dispersing agent:                                                                        Organic dispersing agent:                                  very small amount  very small amount                                                             Surface-active agent:                                                         small amount                                               Water: remaining portion                                                                         Water: remaining portion                                   ______________________________________                                    

In the apparatus shown in FIG. 2, the carbon slurry 14 within the carbonslurry tank 13 is conveyed to the supplying-system pipe 16 by pump 18through the filter 19 to the nozzle section 17. From the nozzle section17, the carbon slurry 14 is ejected onto the inner surface of therotating panel 11 and is uniformly coated thereon to a predeterminedfilm thickness. The extra carbon slurry 14 ejected onto the panel 11 isstored in the lower portion of the cover member 20 and collected intothe carbon slurry tank 13 through the collecting-system pipe 21 by thepump 22. At that time, the collected carbon slurry 14 is passed throughthe column 29 filled with the negative ion-exchange resin located behindthe filter 23 so that boric acid mixed into the collected carbon slurrycan be chemically removed with the result that the viscosity of thecollected carbon slurry is decreased. That is, the carbon slurry isregenerated and then returned to the carbon slurry tank 13.

In this way, the carbon slurry 14 is regenerated and used repeatedly andcyclically without any significant increase in slurry viscosity over thecourse of these cycles. When the amount of the carbon slurry 14 withinthe carbon slurry tank 13 becomes less than a predetermined amount,fresh carbon slurry 14 is supplied into the carbon slurry tank 13 fromsupply pipe 24.

Practical examples of regenerating collected carbon slurry by the use ofnegative ion-exchange resin will be described next.

EXAMPLE 1

Carbon slurry whose viscosity was increased after the carbon slurry 14was ejected onto and uniformly coated on the inner surface of thecathode ray tube panel 11 having the resist layer which underwent thehardening-treatment by the boric acid was collected and then regeneratedby the column 29 filled with a strong base negative ion-exchange resinthat was made by Rohm and Haas Co., Ltd. The collected carbon slurrybefore being regenerated contained boric acid at a concentration of 200ppm. The resulting viscosity of the collected carbon slurry wasincreased by about four times that of fresh carbon slurry. While theregenerated carbon slurry contained 0.5 ppm boric acid after theregeneration, the viscosity of the regenerated carbon slurry was loweredback to its original value. Thus, regenerated carbon slurry could beused again in the carbon-coating process similarly to fresh carbonslurry.

EXAMPLE 2

A regeneration-treatment similar to that described in Example 1 wasperformed. The negative ion-exchange resin filled into the column 29 wasa boric acid selective, weak base negative ion-exchange resin, such as aboric acid, selective chelate resin that was made by Rohm and Haas Co.,Ltd. After the collected carbon slurry in this example was passedthrough the ion exchange resin, the collected carbon slurry wasregenerated.

The negative ion-exchange resin in column 29 from Examples 1 and 2 canbe repeatedly used after being treated by an aqueous caustic sodasolution.

While in the embodiment of the present invention shown in FIG. 2, thecolumn 29 filled with the negative ion-exchange resin is located in themidst of the collecting-system pipe 21, column 29 may also be located inthe midst of the supplying-system pipe 16. The effect of theregeneration-treatment may also be achieved by supplying the negativeion-exchange resin directly into the carbon slurry tank 13. Further, thenegative ion-exchange resin may simultaneously be provided at aplurality of places, for example, in the collecting-system pipe 21, thesupplying-system pipe 16 and the carbon slurry tank 13.

While in the above-mentioned embodiment in which aqueous the boric acidsolution is used as a hardening-treatment agent for the resist layer,the boric acid is mainly removed from the collected carbon slurry by theion-exchange resin. Thus, the collected carbon slurry is regenerated. Itis part of our invention, however, that even when otherhardening-treatment agents (for example, a tannic acid aqueous solution)are used, the collected carbon slurry can be regenerated by means of anion-exchange resin.

According to the method of regenerating carbon slurry used to produce ablack matrix-type phosphor screen, the hardening-treatment agent orother aggregation causing agent contained in the collected carbon slurrycan be removed by passing the collected carbon slurry through theion-exchange resin so that the viscosity of the carbon slurry can bereduced to the viscosity of fresh carbon slurry. Therefore, thecollected carbon slurry can be used again.

Moreover, according to the apparatus for producing a black matrix-typephosphor screen of the present invention, since the carbon slurryregenerating means using the ion-exchange resin is provided in at leastone of the supplying system, collecting-system of the carbon slurry andthe carbon slurry tank, the collected carbon slurry can be regeneratedand hence the carbon slurry can be used cyclically. Therefore, the wasteconsumption of the carbon slurry can be decreased and hence, themanufacturing cost of the black matrix-type phosphor screen of a cathoderay tube can be decreased.

It should be understood that the above description is presented by wayof example on a single preferred embodiment of the invention and it willbe apparent that many modifications and variations thereof could beeffected by one with ordinary skill in the art without departing fromthe spirit and scope of the novel concepts of the invention so that thescope of the invention should be determined only by the appended claims.

We claim:
 1. A method for regenerating a carbon slurry used to produce ablack matrix-type phosphor screen of a cathode ray tube which comprisesthe steps of: (a) collecting excess carbon slurry remaining after thecompletion of a carbon-coating process onto a cathode ray tube panel;and, (b) regenerating said collected carbon slurry by contacting it withan ion-exchange resin.
 2. A method according to claim 1, in which saidion-exchange resin is a negative ion-exchange resin.
 3. A methodaccording to claim 2, in which said negative ion-exchange resin is astrong base negative ion-exchange resin.
 4. A method according to claim3, in which said negative ion-exchange resin is a boric acid selectiveweak base negative ion-exchange resin.
 5. A method according to claim 4,in which said boric acid selective weak base negative ion-exchange resinis a boric acid selective chelate resin.